A lateral diffusion MOS transistor (LDMOS) transistor is a semiconductor device with a lateral current path formed on the surface of semiconductor substrate by planar diffusion. Compared with other MOS transistors, a lightly doped region between the source region and the drain region in the LDMOS transistor is formed. The lightly doped region is referred to as a drift region. When a high voltage is applied between the source region and the drain region of the LDMOS transistor, the drift region is able to withstand a high voltage. Therefore, the LDMOS transistor may have a higher breakdown voltage.
An LDMOS transistor is compatible with CMOS process, so LDMOS transistors can be widely used in the power devices. The on-resistance (Rdson) and the breakdown voltage (BV) are two important indicators in determining the device performance.
An LDMOS transistor includes a source region and a drain region in the semiconductor substrate, and a channel region between the source region and the drain region. A gate electrode is located over the channel region. In addition, different from a field effect transistor, the distance between the drain region and the gate electrode in the LDMOS transistor is greater than the distance between the source region and the gate electrode. The drain region is located in a doped well used to separate the channel region and the drain region.
In order to improve the performance of the LDMOS transistor, reduced surface electric field (RESURF) technique and thin epitaxy (EPI) or N-well region are often used in the LDMOS transistor, to increase the breakthrough voltage and decrease the on-resistance.
However, the breakdown voltage of a conventional LDMOS transistor needs to be improved. The disclosed semiconductor device and fabrication method are directed to solve one or more problems in the art.